Accurate measurements of physiological parameters of the esophagus under realistic swallowing conditions are valuable in diagnosing esophageal diseases such as gastroesophageal reflux disease (GERD), abnormal functioning of the lower esophageal sphincter (LES) and peristaltic muscular contractions and movements in the esophagus, and the like. When a person with a healthy esophagus swallows, circular muscles in the esophagus contract. The contractions begin at the upper end of the esophagus and propagate downwardly toward the lower esophageal sphincter (“LES”). These muscular contractions are commonly called peristaltic movements, contractions, or waves, or simply as “peristalsis”. The function of the peristaltic muscle contractions, i.e., to propel food and drinks through the esophagus to the stomach, is sometimes called the motility function, but is also often used to refer to peristalsis. Therefore, the terms “motility” or “motility function” and “peristalsis” are sometimes used interchangeably.
The LES is normally closed, but it opens momentarily, when a peristaltic contraction approaches it, to admit the bolus of food or drink into the stomach. As a peristaltic contraction passes through each point along the esophagus, the esophageal pressure at that point rises to a maximum and then falls back to a base pressure at the relaxed state. This peristaltic propagation of the esophageal contraction tends to propel any swallowed volume of mass, which is called a “bolus”, ahead of the point of peak pressure and down the esophagus toward the stomach. The motility function of the esophagus, i.e., the esophagus' ability to move a mass, is dependent on several factors, including the peristaltic pressure profile and the characteristics of the esophageal muscles.
Esophageal pressure measurement, or manometry, as well as electrical impedance have been used to assess motility function of the esophagus and bolus transit dynamics in the esophagus. A typical esophageal manometer includes an elongated catheter or probe with pressure sensors located along its length. The catheter or probe is designed to be inserted into the esophagus, typically reaching the LES and extending into the stomach, of a patient, with the pressure sensors positioned at the LES and at a plurality of other specific points along the length of the esophagus at predetermined distances above the LES. During a typical test, the patient swallows a specific amount of water with the manometer placed in the esophagus. The esophageal pressure at the pressure sensors can be measured and used as an indication of the magnitude and sequence of the peristaltic contractions. In addition, because the positions of the sensors are known, the velocity of the peristaltic motion can also be ascertained from the location of the peak pressure as a function of time. The test can be repeated a number of times to obtain a set of pressure and velocity values, a statistical analysis of which may be used for diagnostic purposes. For example, according to one protocol, ten 5-ml water swallows are to be performed at approximately 30-second intervals. The patient's functional response is determined as a percentage of the swallows. For example, a result of such test swallows may show that 80% of the swallows were followed by a contraction pressure of 30 mmHg or greater with an onset velocity of about 8 cm/sec, and, therefore, showed normal peristalsis; the remaining 20% of the swallows resulted in a contraction pressure of less than 30 mmHg and, therefore, are deemed to be ineffective peristalsis.
While the conventional manometry (pressure measurements) is useful for assessing certain aspects of the physiology of the esophagus, i.e., peristaltic muscular activity in the esophagus and LES are detectable as pressure changes, the technique has its limitations in at least two respects. Esophageal manometry does not measure or predict bolus transit, which is the actual movement of a mass of swallowed material through the esophagus. Esophageal peristalsis generally is triggered by a swallowing action and proceeds whether or not any substance is actually swallowed, and the peristaltic muscular contractions may proceed regardless of whether the bolus is actually moving through the esophagus. Further, some swallowed material, such as water, will flow by gravity through the esophagus, even if there are no peristaltic muscular contractions or if they are irregular or erratic. Thus, the mere manometric detection of propagating peristaltic muscular contractions, even if they are properly timed and of normal amplitude (strength), does not necessarily mean that any bolus is being propelled by the peristalsis. Thus, incomplete bolus transit may not be detected by manometry alone. Other substances could be swallowed, such as food, but resulting data, such as impedance, would vary, depending on the characteristics of the food or other substances.
Electrical impedance at a plurality of points in the esophagus can be used to detect and monitor movement of a bolus through the esophagus. Essentially, a bolus of water or food will have different electrical impedance than the non-filled esophagus, so a change in impedance in the esophagus indicates presence of a bolus. Therefore, an elongated probe positioned in the esophagus with a plurality of impedance and/or acidity sensors dispersed along its length can be used to detect and monitor the bolus transit, i.e., the movement of a bolus through the esophagus. Therefore, by combining manometry (pressure measurements) with simultaneous impedance measurements, both peristalsis and bolus transit can be quantified, and these measurements, if accurate and dependable, can be combined to determine whether the bolus movement and the peristaltic contractions are in proper synchronization or if there is an abnormal or dysfunctional relationship between them.
Unfortunately, prior to this invention, it was very difficult, if not impossible, to get consistent, accurate, reliable, and repeatable impedance measurements, even if the impedance probes, sensors, and measuring equipment, itself, was well-designed and in good working condition. The problem was that the swallow media available for such tests were inadequate. For example, water as a medium for swallow tests provides very little resistance to peristaltic propulsion and is often inadequate to cause esophageal abnormalities to manifest themselves during the test. Water also has inconsistent ionic content, varying from one source to another or from one municipal water system to another, which causes variations in impedance measurements and is often insufficient to even make meaningful impedance measurements. Saline solution has more ionic content, but it provides insufficient resistance to peristaltic propulsion to cause esophageal abnormalities to be detected. Water and saline solution also do not remain in a distinct, well-defined bolus mass and, instead, run and spread by gravity through the length of the esophagus, bridging many or all of the impedance sensor electrodes so that sensing distinct bolus transit dynamics in relation to manometric detection of peristalsis is difficult, if not impossible. Other substances, such as yogurt, mash potatoes, or other foods could be swallowed, but resulting data, such as impedance, would vary, depending on the physical characteristics of the foods, such as ionic content, viscosity, surface tension, and the like. Also, foods tend to coat or stick to the probe and impedance sensor electrodes on the probe, even after the bolus has passed, which interferes with subsequent impedance measurements and makes it difficult and often impossible to detect bolus transit in subsequent swallows. These and other deficiencies contribute to erratic, inconsistent, unreliable, and unrepeatable test results.
A state-of-the-art technique for observing and assessing actual bolus transit includes a barium esophagram diagnostic test, in which a patient in front of an X-ray camera performs swallows of a contrast medium that shows distinctly in an X-ray image. This diagnostic method, however, has a number of drawbacks as well, including the high cost of equipment and exposure of patients to ionizing radiation, and it is not conducive to ambulatory testing. In addition, manometric data synchronized with bolus transit are not available from barium esophagram tests. Such synchronized data is often important in assessing the complex physiology of bolus transit dynamics.